We report on a BeppoSAX Concentrator Spectrometer observation of the
super-soft source (SSS) CAL87. The X-ray emission in SSS is believed to arise
from nuclear burning of accreted material on the surface of a white dwarf (WD).
An absorbed blackbody spectral model gives a chi^2_v of 1.18 and a temperature
of 42 +/- ^13 _11 eV. However, the derived luminosity and radius are greater
than the Eddington limit and radius of a WD. Including an O viii edge at 0.871
keV gives a significantly better fit (at > 95% confidence) and results in more
realistic values of the source luminosity and radius. We also fit WD atmosphere
models to the CAL87 spectrum. These also give reasonable bolometric
luminosities and radii in the ranges 2.7-4.8 10^{36} erg/s and 8-20 10^7 cm,
respectively. These results support the view that the X-ray emission from CAL87
results from nuclear burning in the atmosphere of a WD.Comment: 4 pages. Accepted for publication in A&A (Letters